Note: Descriptions are shown in the official language in which they were submitted.
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Rail with Reduced Radiated Noise Level
The invention relates to a profiled rail, especially a railway rail, having a
reduced total radiated noise level when in use, and comprising a foot
section with a bottom surface, a web section, and a head section with a
tread surface, and having a rail height and preferably also a rail head width,
and in particular a moment of inertia and a section modulus about the axis
of the centre of gravity, corresponding substantially to those of standard,
normally profiled rails having the same load-bearing capacity.
Running rails are profiled, rolled steel bars which are used to build
trackways, especially railroad tracks, on which loads can be economically
transported. On these tracks, metallic wheels, made preferably from steel or
having a steel tire, run on the tread surface of a section of the rail
referred
to as the rail head. The foot of the rail, which is located opposite to and
joined to the head by means of a web, is connected with its bottom surface
to a base structure.
In the course of development of railway systems, functionally optimized
cross-sectional profiles of rails were appropriately standardized for various
loads and applications. In Europe, a frequently used standard profile for
railroad rails bears the designation UIC 60; the rail weighs approx. 60 kg/m
and tight dimensional tolerances of, for example, ~ 0.6 mm for the rail
height and ~ 0.5 mm for the width of the rail head, are specified. Tight
tolerances in the rail profile are important, especially for the purpose of
building a geometrically accurate track intended to permit the speed of
trains to be increased without any loss in ride comfort and without any
major dynamic loads occurring. In order to reduce wear, rails having heads
exhibiting increased hardness are already being manufactured and used.
Despite the highest possible dimensional accuracy, a tread or running
surface of the best quality, and smoothness of the rails, as railway cars
travel along the track vibrations, and thus radiated noise, occur. This
airborne noise can attain high intensity, especially at high transportation
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speeds, and it can cause considerable environmental pollution. It has been
found that the travel noise generated by trains is caused to a considerable
extent by airborne noise radiated from the surface of the rail.
Attempts have already been made by sound-insulating surface sections of
the rail to reduce the intensity of the radiated noise.
Applying a coating of vibration-damping material, as proposed in DE-A-
4225581 or AT-AS 652/90, is only partially successful in achieving this
goal; it is also expensive, prevents visual inspection of the rail in the
track
and, especially if reinforced polymers are used, it can itself be a source of
environmental pollution. In addition, there have been several proposals, e.g.
in DE-OS 441 1833, to use elastic components in the fastening elements to
reduce the transmission of vibrations to the base structure and thus to
reduce the amount of airborne noise radiated from this source.
All the devices and arrangements so far proposed to reduce the airborne
noise radiated from rails or track installations have in common the
disadvantage that they are not very effective, and/or are very expensive,
and are aimed essentially at reducing the transmission of vibrations from the
rail.
It is the purpose therefore of the invention to reduce or shape the vibration
of the rail, when it is travelled on by trains moving especially at high
transportation speeds, so that the total level of radiated noise and the noise
pollution of the environment are reduced. The goal of the invention is thus
in particular to reduce the vibrations of the body or the rail itself, which
vibrations are responsible for generating the airborne noise, and thereby, in
a simple manner, to reduce the radiated noise and the environmental
pollution.
Using a profiled rail of the kind mentioned at the beginning, this task or
goal
is accomplished in that at least one lateral web surface, at least in the
lower
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area between the transition edge at the foot of the rail, namely the edge
formed at the transition from the foot into the lateral web surface, on the
one hand, and the axis of the centre of gravity, on the other hand, is
concavely rounded and substantially free of any angularities in the cross
section of the rail, and/or the height of the rail foot is larger compared
with
that of a standard profiled rail.
It has surprisingly been discovered that, contrary to what is assumed by
experts in the field, it is not the web between the head and foot of the rail,
vibrating like a membrane, that creates most of the radiated noise. Instead,
the rail head and in particular the foot of the rail exhibit high solid-borne
noise levels and thus contribute greatly to the level of the total sound
pressure and in turn are chiefly responsible for the noise pollution of the
environment. The reasons for the increased wave-like vibration in the
longitudinal direction, i.e. the springiness, as a function of the frequency,
for example, of one flange of a rail foot have not yet been scientifically
fully
explained. However, it is assumed that angularities in the surface profile or
discontinuous changes in the thickness of the cross section may act as
vibration nodes or theoretical clamping points causing or permitting
increased vibrations to occur in sections of the rail profile, for example in
a
flange of the rail foot. In the manner according to the invention, increasing
the height of the foot of the rail and/or in particular ensuring the
transition,
without angularities, from the foot into the lateral surface of the web brings
about a change in the vibrations in the area of the rail foot; as a result,
the
amount of airborne noise radiated by the surfaces of the rail foot into the
environment and possibly to a base structure which reflects this radiated
noise, is reduced.
A further reduction in the radiated noise is achieved when the cross-
sectional profile is designed symmetrically to the height axis, as a result of
which the tendency for local vibration nodes to form in the profiled bar is
further reduced.
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If, as further advantageously provided, the lower part and the upper part of
the lateral surface of the rail web between the transition edge at the foot of
the rail and the transition edge at the head of the rail, namely the edge
which is formed when the lateral surface of the rail head merges into the
upper surface of the web, are designed so as to be concavely rounded and
substantially free of angularities in the cross section of the rail, the
formation of vibrations, especially in sections of the rail profile which as a
result radiate airborne noise, is further reduced.
It may be further advantageous from the point of view of manufacturing or
rolling the rail, as well as for the purpose of minimizing the weight, but
especially also in order to reduce airborne noise emission, if in the cross
section of the rail the lateral surface of the rail web is made up of a
circularly and/or an elliptically shaped lower and upper part and possesses
preferably a straight middle or intermediate section, merging tangentially
with the aforesaid parts, and through this middle section passes the axis of
the centre of gravity. It may be favourable in this case if the minimum
thickness of the rail web is the same as or greater than that of standard
rails.
A particularly favourable embodiment, in which the rail possesses a high
load-bearing capacity while at the same time radiating a low level of
airborne noise is achieved if the distance between the axis of the centre of
gravity and the bottom surface at the foot of the rail has a value between
(0.5 and 0.38), preferably between (0.47 and 0.41 ) times the height (A) of
the rail.
The vibration sensitivity of the outer sections of the flanks of the rail foot
can be largely eliminated or minimized in a simple way if the foot is less
wide and/or higher compared with the respective standard rail profile.
If, as advantageously provided, the hardness of the material in the head,
and in particular in the tread area of the rail according to the invention,
has
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been increased, as known in the art, it is possible to substantially reduce
the
resulting increase in the noise radiated by standard profiles if, in addition,
the hardness of the material in the foot and in particular in the central area
of the rail, which is arranged substantially symmetrically to the axis of the
rail and contains the bottom surface, is also increased; in this way, a
particularly stable embodiment possessing ideal functional properties is
obtained.
In the following, the invention is explained in more detail based on methods
of implementation and test results schematically illustrated in the drawings.
Figure 1 is a cross section through a standard UIC 60 rail.
Figure 2 is a cross section through a rail reinforced according to the
invention in the foot area.
Figure 3 is the cross section through a rail having rounded lateral web faces,
free of angularities, at the foot of the rail.
Figure 4 is a rail cross section with fully rounded web surfaces.
Figure 5 depicts the total level of solid-borne noise and the weights of rails
as a function of the cross-sectional shape.
Figure 1 shows a cross-sectional view of a standard UIC 60 rail. The rail has
an overall height A of 172 mm, a head height of 37.55 mm from the tread
surface 41 to the edge 34 where the transition is made from the side 42 of
the head 1 to a lateral surface 31 of the web, and a foot width B of 150 mm.
The distance S of the axis X of the centre of gravity from the bottom surface
21 extending between side edges 22 at the foot 2 of the rail is 80.95 mm.
A standard UIC 60 rail of this type, having a weight or mass of 60.84 kg/m,
was caused to vibrate by applying excitation in the form of impulses
laterally or eccentrically at the tread surface 41, transverse to the
longitudinal orientation, in a vertical and horizontal direction, and the
maximum total level of solid-borne noise as well as the radiated sound
power were determined. The values determined for a standard rail, as
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shown in Fig. 5, bar B, represent base values for the UIC 60 which can be
compared with the values obtained from rails according to the invention.
Figure 2 depicts a rail according to the invention having a reinforced foot 2,
or a larger foot thickness H, compared with a standard UIC 60 rail. As a
result, while maintaining the same overall rail height A, the distance S
between the axis (X) of the centre of gravity and the bottom surface 21 is
reduced and, as is also apparent from Figure 5, bar 1, the weight of the rail
is slightly increased. Compared with a standard rail, given the same
excitation, this design leads to a reduction in the maximum total level of
solid-borne noise and to a significant drop in the total level of airborne
noise, as is also evident from Figure 5, bar 1.
Figure 3 shows a rail profile according to the invention in which the foot 2
has a height H corresponding to the standard UIC 60 profile, but in which
the lower part 31' of the lateral surface 31 of the rail web 3, between the
transition edge 32 at the foot and the intersection with the axis X of the
centre of gravity, has a symmetrical, circularly rounded configuration free of
angularities. Compared with the standard rail, when the same pulsating
excitation was applied, this embodiment was found to have a much reduced
total level of solid-borne noise and a total level of radiated sound power
that
was lower by approximately 1.05 dB, as shown diagrammatically in Figure
5, bar 2, while the mass of the rail (see lower part of Figure 5, bar 2) was
only slightly increased.
Figure 4 shows another rail profile according to the invention which
possesses fully rounded fishing spaces, or lateral web surfaces 31 free of
angularities, extending from the transition edge 32 at the foot of the rail to
the transition edge 34 at the head of the rail, and having a plane-parallel
middle section of the web 3 in the area of the axis of the centre of gravity,
said section merging tangentially into said surfaces. A continuous thickening
of the web 3 towards the head 4 and the foot 2 of the rail increases the
mass of the rail 1 per metre, as is evident from the lower part of Figure 5,
bar 3. As also shown by bar 3 in the upper part of Figure 5, the maximum
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total level of solid-borne noise is reduced to a very small percentage
compared with the standard UIC 60 profile, and also the total level of
radiated sound power is reduced by about 3.0 dB.
Compared with other standard rail profiles, rails embodying the
characteristics according to the invention also exhibited substantially lower
total levels of radiated sound power.
